/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.discovery.jdk;

import java.io.IOException;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;

import org.apache.commons.discovery.log.DiscoveryLogFactory;
import org.apache.commons.logging.Log;

/**
 * @author Richard A. Sitze
 */
public class JDK12Hooks extends JDKHooks {

  /**
   * Logger
   */
  private static Log log = DiscoveryLogFactory.newLog(JDK12Hooks.class);

  private static final ClassLoader systemClassLoader = findSystemClassLoader();

  static private ClassLoader findSystemClassLoader() {
    ClassLoader classLoader;

    try {
      classLoader = ClassLoader.getSystemClassLoader();
    } catch (SecurityException e) {
      /**
       * Ignore and keep going.
       */
      classLoader = null;
    }

    if (classLoader == null) {
      SecurityManager security = System.getSecurityManager();
      if (security != null)
        try {
          security.checkCreateClassLoader();
          classLoader = new PsuedoSystemClassLoader();
        } catch (SecurityException se) {
        }
    }

    // Return the selected class loader
    return classLoader;
  }

  private static Enumeration<?> getResourcesFromUrl(final URL first,
      final Enumeration<?> rest) {
    return new Enumeration<Object>() {
      private boolean firstDone = first == null;
      private URL next = getNext();

      private URL getNext() {
        URL n;

        if (!firstDone) {
          /**
           * First time through, use results of getReference() if they were
           * non-null.
           */
          firstDone = true;
          n = first;
        } else {
          /**
           * Subsequent times through, use results of getReferences() but take
           * out anything that matches 'first'.
           * 
           * Iterate through list until we find one that doesn't match 'first'.
           */
          n = null;
          while (rest.hasMoreElements() && n == null) {
            n = (URL) rest.nextElement();
            if (first != null && n != null && n.equals(first))
              n = null;
          }
        }

        return n;
      }

      public boolean hasMoreElements() {
        return next != null;
      }

      public Object nextElement() {
        URL o = next;
        next = getNext();
        return o;
      }
    };
  }

  /**
   * Must be implemented to use DiscoveryLogFactory
   */
  public static void setLog(Log _log) {
    log = _log;
  }

  /**
   * Implement ClassLoader.getResources for JDK 1.2
   */
  @Override
  public Enumeration<?> getResources(ClassLoader loader, String resourceName)
      throws IOException {
    /**
     * The simple answer is/was: return loader.getResources(resourceName);
     * 
     * However, some classloaders overload the behavior of getResource
     * (loadClass, etc) such that the order of returned results changes from
     * normally expected behavior.
     * 
     * Example: locate classes/resources from child ClassLoaders first, parents
     * last (in some J2EE environs).
     * 
     * The resource returned by getResource() should be the same as the first
     * resource returned by getResources(). Unfortunately, this is not, and
     * cannot be: getResources() is 'final' in the current JDK's (1.2, 1.3,
     * 1.4).
     * 
     * To address this, the implementation of this method will return an
     * Enumeration such that the first element is the results of getResource,
     * and all trailing elements are from getResources. On each iteration, we
     * check so see if the resource (from getResources) matches the first
     * resource, and eliminate the redundent element.
     */

    final URL first = loader.getResource(resourceName);

    // XXX: Trying to avoid JBoss UnifiedClassLoader problem

    Enumeration<?> resources;

    if (first == null) {
      log.debug("Could not find resource: " + resourceName);
      resources = Collections.enumeration(Collections.EMPTY_LIST);

    } else {

      try {

        resources = loader.getResources(resourceName);

      } catch (RuntimeException ex) {
        log.error("Exception occured during attept to get " + resourceName
            + " from " + first, ex);
        resources = Collections.enumeration(Collections.EMPTY_LIST);
      }

      resources = getResourcesFromUrl(first, resources);
    }

    return resources;
  }

  /**
   * The system class loader is available for JDK 1.2 or later, if certain
   * security conditions are met.
   * 
   * @return The system class loader, if available. Otherwise return null.
   */
  @Override
  public ClassLoader getSystemClassLoader() {
    return systemClassLoader;
  }

  /**
   * Get the system property
   * 
   * @param propName
   *          name of the property
   * @return value of the property
   */
  @Override
  public String getSystemProperty(final String propName) {
    return (String) java.security.AccessController
        .doPrivileged(new java.security.PrivilegedAction<Object>() {
          public Object run() {
            try {
              return System.getProperty(propName);
            } catch (SecurityException se) {
              return null;
            }
          }
        });
  }

  /**
   * The thread context class loader is available for JDK 1.2 or later, if
   * certain security conditions are met.
   * 
   * @return The thread context class loader, if available. Otherwise return
   *         null.
   */
  @Override
  public ClassLoader getThreadContextClassLoader() {
    ClassLoader classLoader;

    try {
      classLoader = Thread.currentThread().getContextClassLoader();
    } catch (SecurityException e) {
      /**
       * SecurityException is thrown when a) the context class loader isn't an
       * ancestor of the calling class's class loader, or b) if security
       * permissions are restricted.
       * 
       * For (a), ignore and keep going. We cannot help but also ignore (b) with
       * the logic below, but other calls elsewhere (to obtain a class loader)
       * will re-trigger this exception where we can make a distinction.
       */
      classLoader = null; // ignore
    }

    // Return the selected class loader
    return classLoader;
  }
}
